There are various ways to make gaskets, and economics play a big part in determining which mode of fabrication is most suitable for a given end product. A large share of gaskets manufactured are made from sheet packing, being die-cut to appropriate shape, and then additionally processed to meet specific requirements. For example, as shown in Farnam U.S. Pat. No. 3,661,401, the packing material was selected for all of the requisite physical properties needed except for sealability, and then the gasket was encapsulated or coated with a suitable coating material to provide that property.
Again, in Farnam et al. U.S. Pat. No. 3,655,210, a special gasket structure comprising a core having special heat insulating bushings at the bolt holes, and covered on both sides with packing material, was compressed to provide an upstanding bead in the packing material for desired sealability.
Molded rubber gaskets, with or without sealing beads, are well known in the art.
Convolutely wound gaskets have had a limited application because it has been generally assumed that once the gasket is cut from the convolute tube from which is was made, it was a completed gasket except for possible post-curing.
The present invention provides a new horizon for convolute gaskets by teaching the manner in which they may be wound with appropriate materials and under appropriate conditions to form a basic gasket structure and shape, after which they are processed through the application of lateral pressure to provide the desification required for torque retention, and simultaneously with the desification a bead of lesser density may be formed, and optionally the gasket structure thus fabricated may then be coated on the top and bottom faces or completely encapsulated to provide desired sealing quality.
The prior art discloses conventional gaskets that are provided with sealing beads but which are of the same density and compressibility as the unbeaded portions of the gaskets. All of these prior gaskets are of limited use because of specific functional properties. Some jointing requirements are adequately met by providing a gasket with a molded bead on one or both sides of the gasket to create a more comformable seal than could be created with the same material unbeaded, and these gaskets were usually made from solid elastomeric materials. This type of gasket structure offered relatively poor torque retention, while distortion of the mating surfaces was substantially uncontrolled and the physical properties were quite restricted because of the limited materials that could be formed into this type of gasket structure.
The prior art also includes some instances where gaskets and like articles have been formed by making rubber tubes by winding rubber stock on a mandrel or by extruding such stock in the form of a tube and thereafter curing the formed rubber tube after which gaskets are cut from the tube. One facet of the present invention, however, includes an improvement for controlling the thickness of the wound tube as reflected in the final gasket product and the novel convolute beaded disclosed herein incorporates this improvement.
A need exists for a beaded gasket structure that can be manufactured economically to fit the numerous applications that are subject to substantial distortion under clamping loads and which require high torque retention directly under and between the clamping bolts, since the gasketing of clamped faces is usually an economic compromise that is answered by the provision of a joint that can be sealed and then opened and re-sealed many times at the lowest possible cost which embraces the structure and shape of the clamping faces, the number, size and type of fasteners, the quality of flange smoothness and flatness, as well as other factors.